Charlottesville, Va.

Marketers are spending 26 percent more on paid search this year, if they're anything like search and digital marketing agency RKG's clients. The Charlottesville, Va.-based agency, a Merkle company, released findings comparing Q3 2014 results with those from Q3 2013.

A few weeks ago, my teenage daughter and I drove from Charlottesville, Va., to Boston on a 1,200-mile college tour. At each college we visited, we were handed beautiful brochures to match the equally beautiful campuses. Each school had taken great pains to maximize their image -- or brand -- in an effort to impress tens of thousands of prospective students, even though they will actually accept only a small fraction of them.

While there aren't too many elements within a paid search listing to test, there are myriad front-end and back-end variables that affect results-from search engine to ranking, landing page to conversion process.

The following are a few metrics search experts find indispensable to determining the effectiveness of paid search programs.